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General Chemistry Principles, Patterns, and Applications, 2011

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Studies on fruit flies show a linear<br />

relationship between the number of genetic defects <strong>and</strong> the magnitude of the radiation dose <strong>and</strong><br />

exposure time, which is consistent with a cumulative effect of radiation. In contrast, studies on mice<br />

show an S-shaped curve, which suggests that the number of defects is lower when radiation<br />

exposure occurs over a longer time. Which of these relationships is more applicable to humans is a<br />

matter of considerable debate.<br />

Summary<br />

The effects of radiation on matter depend on the energy of the radiation.Nonionizing radiation is<br />

relatively low in energy, <strong>and</strong> the energy is transferred to matter in the form of heat. Ionizing<br />

radiation is relatively high in energy, <strong>and</strong> when it collides with an atom, it can completely remove an<br />

electron to form a positively charged ion that can damage biological tissues. Alpha particles do not<br />

penetrate very far into matter, whereas γ rays penetrate more deeply. Common units of radiation<br />

exposure, or dose, are the roentgen (R), the amount of energy absorbed by dry air, <strong>and</strong> the rad<br />

(radiation absorbed dose), the amount of radiation that produces 0.01 J of energy in 1 kg of matter.<br />

The rem (roentgen equivalent in man) measures the actual amount of tissue damage caused by a<br />

given amount of radiation. Natural sources of radiation include cosmic radiation, consisting of highenergy<br />

particles <strong>and</strong> γ rays emitted by the sun <strong>and</strong> other stars;cosmogenic radiation, which is produced<br />

by the interaction of cosmic rays with gases in the upper atmosphere; <strong>and</strong> terrestrial radiation, from<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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